In the given figure of meter bridge experiment, the balancing length $AC$ corresponding to null deflection of the galvanometer is $40\,cm$. The balancing length, if the radius of the wire $AB$ is doubled, will be $….cm$

In a meter bridge the point $D$ is neutral point as shown in the figure.

What are the advantages of the null-point method in a Wheatstone bridge ? What additional measurements would be required to calculate ${{\rm{R}}_{{\rm{unknown}}}}$ by any other method ?

During an experiment with a metre bridge, the galvanometer shows a null point when the joceky is pressed at $40.0 \ cm$ using a standard resistance of $90 \ \Omega$, as shown in the figure. The least count of the scale used in the meter bridge is $1 \ mm$. The unknown resistance is:

The resistance per centimeter of a meter bridge wire is $\mathrm{r}$, with $\mathrm{X}\  \Omega$ resistance in left gap. Balancing length from left end is at $40 \mathrm{~cm}$ with $25\  \Omega$ resistance in right gap. Now the wire is replaced by another wire of $2 \mathrm{r}$ resistance per centimeter. The new balancing length for same settings will be at